The present invention relates to an apparatus and method for removing hysteresis of motor driven power steering (MDPS), and more particularly, to an apparatus and method for removing hysteresis of MDPS, which applies a current having an asynchronous frequency, which does not coincide with a synchronous frequency of a motor, to the motor at high speed within a short time, thereby removing hysteresis of a current sensor which measures the current applied to the motor.
The MDPS may include an electronic control unit (ECU) which receives signals of various sensors such as a torque sensor and various signals within a vehicle, generates a control command containing one or more of a torque command and a current command, transfers the control command to a motor control device within the ECU, and performs torque control for a motor based on the control command.
At this time, real-time feedback information on a rotation state and a load current of the motor may be required to perform the torque control for the motor. In this case, a current sensor of the motor may be used.
That is, the current sensor may convert the magnitude of a motor current corresponding to an actual current flowing in the motor into an induced magnetization, and outputs the induced magnetization as a voltage or current.
However, when the current applied to the motor becomes zero by the property of the current sensor, the induced magnetization may not converge to zero, but hysteresis may remain to thereby generate a current offset deviation.
Thus, a driving device for MDPS has been conventionally designed to compensate for a ripple characteristic corresponding to hysteresis through an algorithm. However, when the MDPS is driven at a light load or large hysteresis remains, a torque ripple or current offset deviation cannot be removed through the conventional compensation algorithm.
That is, even when the ECU is powered off, hysteresis may partially remain. Then, when the ECU is powered on, the remaining hysteresis may generate a current offset deviation. The generated current offset may distort a zero current, and add to a torque ripple caused by a pole/slot combination of the motor.
Thus, the MDPS may be seriously affected by the torque ripple caused by the hysteresis remaining in the current sensor, during current control. Therefore, there is a demand for the development of technology for removing hysteresis.
The related art of the present invention is disclosed in Korean Patent Laid-open Publication No. 10-2010-0091770 published on Aug. 19, 2010 and entitled “Method and apparatus for controlling motor”.